Dr. Manfred Stähli

Although rainfall-triggered landslides are initiated by subsurface hydro-mechanical processes related to the loading, weakening, and eventual failure of slope materials, most landslide early warning systems (LEWSs) have relied solely on rainfall event information. In previous decades, several studies demonstrated the value of integrating proxies for subsurface hydrologic information to improve rainfall-based forecasting of shallow landslides. More recently, broader access to commercial sensors and telemetry for real-time data transmission has invigorated new research into hydrometeorological thresholds for LEWSs. Given the increasing number of studies across the globe using hydrologic monitoring, mathematical modeling, or both in combination, it is now possible to make some insights into the advantages versus limitations of this approach. The extensive progress demonstrates the value of in situ hydrologic information for reducing both failed and false alarms through the ability to characterize infiltration during – as well as the drainage and drying processes between – major storm events. There are also some areas for caution surrounding the long-term sustainability of subsurface monitoring in landslide-prone terrain, as well as unresolved questions in hillslope hydrologic modeling, which relies heavily on the assumptions of diffuse flow and vertical infiltration but often ignores preferential flow and lateral drainage. Here, we share a collective perspective based on our previous collaborative work across Europe, North America, Africa, and Asia to discuss these challenges and provide some guidelines for integrating knowledge of hydrology and climate into the next generation of LEWSs. We propose that the greatest opportunity for improvement is through a measure-and-model approach to develop an understanding of landslide hydro-climatology that accounts for local controls on subsurface storage dynamics. Additionally, new efforts focused on the subsurface hydrology are complementary to existing rainfall-based methods, so leveraging these with near-term precipitation forecasts is a priority for increasing lead times.

It has been widely recognised that the degree of soil wetness before precipitation events can be decisive for whether or not shallow rainfall-induced landslides occur. While there are methods to measure and/or model soil wetness in complex topography, they often exhibit limitations in spatial or temporal resolution, hindering their application in regional landside initiation modelling. In this study, we address the need for high-resolution predictions of initial saturation before rainfall events by employing data-driven linear regression models. The models were trained using in-situ soil moisture data collected from six measurement stations located in a landslide-prone region in Switzerland. Various topographic attributes, along with multiple antecedent rainfall and evapotranspiration variables were tested as input for the models. The final model consisted of five measurable variables, including cumulative antecedent rainfall, cumulative evapotranspiration, and the topographic wetness index (TWI). The model effectively reproduced the observed spatial and temporal variability of the in-situ measurements with a coefficient of determination R² = 0.62 and a root mean square error RMSE = 0.07. Subsequently, we applied the regression model to predict the spatial soil saturation at the onset of actual landslide triggering rainfall events and integrated these patterns into the hydromechanical model STEP-TRAMM. The results demonstrate improvements in predicting observed landslide occurrences compared to simulations assuming spatially uniform initial saturation conditions, highlighting the importance of in-situ measurements and a realistic extrapolation of such data in space and time for accurate modelling of shallow landslide initiation.

Compte tenu des quantités de neige exceptionnelles dans l'ensemble de l'espace alpin, le risque de crues printanières généralisées a été évoqué très tôt au printemps 1999. Ces craintes se sont confirmées en mai, à la suite de deux épisodes de fortes précipitations à l'Ascension et à la Pentecôte. Les grands lacs subalpins - notamment le lac de Thoune et le lac de Constance - ont alors débordé, provoquant des dommages de l'ordre de 580 millions de CHF. La situation de crue tendue qui a duré plusieurs semaines reste dans les mémoires comme la dernière « crue printanière classique de grande ampleur en Suisse » et est considérée jusqu'à aujourd'hui comme l'exemple type d'une combinaison défavorable entre la fonte des neiges à grande échelle et de fortes précipitations. L'analyse globale des événements réalisée à l'époque par la Confédération a mis en évidence la nécessité d'un service hydrologique nivologique professionnalisé (permanent). Celui-ci a été mis en place quelques années plus tard au WSL Institut pour l'étude de la neige et des avalanches SLF et a depuis fait ses preuves.

Angesichts der ausserordentlichen Schneemengen im ganzen Alpenraum wurde bereits zu einem frühen Zeitpunkt im Frühjahr 1999 auf die Gefahr eines verbreiteten Frühlingshochwassers hingewiesen. Diese Befürchtungen bewahrheiteten sich im Mai als Folge von zwei Starkniederschlagsereignissen über Auffahrt und Pfingsten. Dabei traten insbesondere die grossen Alpenrandseen – namentlich der Thunersee und Bodensee – über die Ufer und verursachten Schäden in der Grössenordnung von rund 580 Mio. CHF. Die über mehrere Wochen andauernde angespannte Hochwasserlage bleibt als bisher letztes «klassisches, grossflächiges Frühlingshochwasser der Schweiz» in Erinnerung und gilt bis heute als Musterbeispiel einer ungünstigen Kombination von grossflächiger Schneeschmelze und Starkniederschlägen. Die damalige umfassende Ereignisanalyse des Bundes hat die Notwendigkeit eines professionalisierten (ständigen) schneehydrologischen Dienstes aufgezeigt. Dieser wurde ein paar Jahre später am WSL-Institut für Schnee und Lawinenforschung SLF aufgebaut und hat sich seither bestens bewährt.

Snowpack is an important temporal water storage for downstream areas, a potential source of natural hazards (avalanches or floods) and a prerequisite for winter tourism. Here, we use thousands of manual measurements of the water equivalent of the snow cover (SWE) from almost 30 stations between 1,200 and 2,900 m a.s.l. from four long-term monitoring programs (earliest start in 1937) in the center of the European Alps to derive daily SWE based on snow depth data for each station. The inferred long-term daily SWE time series were analyzed regarding spatial differences, as well as potential temporal changes in variability and seasonal averages during the last 7 decades (1957-2022). The investigation based on important hydro-climatological SWE indicators demonstrates significant decreasing trends for mean SWE (Nov-Apr) and for maximum SWE, as well as a significantly earlier occurrence of the maximum SWE and earlier disappearance of the continuous snow cover. The anomalies of mean SWE revealed that the series of low-snow winters since the 1990s is unprecedented since the beginning of measurements. Increased melting during the accumulation period below 2000 m a.s.l is also observed-especially in the most recent years–as well as slower melt rates in spring, and higher day-to-day variability. For these trends no regional differences were found despite the climatological variability of the investigated stations. This indicates that the results are transferable to other regions of the Alps.

In view of a national Landslide Early Warning System (LEWS) for Switzerland, a pilot study is currently running in the Napf-region (central Switzerland), a hilly semi-forested area (186 km²) with a substantial number of shallow landslide observations in the past decades. The study includes a comprehensive soil wetness monitoring, a test of a numerical model to simulate distributed landslide triggering, as well as the application of Distributed Acoustic Sensing (DAS) at the scale of a steep slope. We show that the applied tools provide a promising basis for a systematic observation, assessment and warning of critical landslide situations. At the same time, this work also suggests that the soil physical conditions can and need to be addressed in an adequate way to correctly rate the spatial and temporal criticality for landslide triggering.

Past studies on the impacts of climate change (CC) on Alpine hydropower production have focused on high-head accumulation power plants. We provide one of the first comprehensive, simulation-based studies on CC impacts on Alpine Run-of-River (RoR) production, also considering effects of environmental flow requirements and technical increase potential. We simulate future electricity production under three emissions scenarios for 21 Swiss RoR plants with a total production of 5.9 TWh a⁻¹. The simulations show an increase in winter production (4 % to 9 %) and a decrease in summer production (−2 % to −22 %), which together lead to an annual decrease of about −2 % to −7 % by the end of the century. The production loss due to environmental flow requirements is estimated at 3.5 % of the annual production; the largest low-elevation RoR power plants show little loss, while small and medium-sized power plants are most affected. The potential for increasing production by optimising the design discharge amounts to 8 % of the annual production. The largest increase potential is related to small and medium-sized power plants at high elevations. The key results are: i) there is no linear relationship between CC impacts on streamflow and on RoR production; the impacts depend on the usable streamflow volume, which is influenced by the Flow Duration Curve, environmental flow requirements, and design discharge; ii), the simulated production impacts show a strong correlation (>0.68) with the mean catchment elevation. The plants at the highest elevations even show an increase in annual production of 3 % to 23 %, due to larger shares of precipitation falling as rain instead of snow. These general results are transferable to RoR production in similar settings in other Alpine locations and should be considered in future assessments. Future work could focus on further technical optimisation potential, considering detailed operational data.

Recent studies have demonstrated the potential of in situ soil wetness measurements to predict regional shallow landslides. Increasing availability of monitoring data from sensor networks provides valuable information for developing future regional landslide early warning systems (LEWSs); however, most existing monitoring sites are located on flat terrain. The question arises of if the representativeness for regional landslide activity would improve if sensors were installed on a landslide-prone hillslope. To address this, two soil wetness monitoring stations were installed at close proximity on a steep slope and on a flat location in the Napf region (Northern Alpine Foreland of Switzerland), and measurements were conducted over a period of 3 years. As both sites inhibit similar lithological, vegetation, and precipitation characteristics, soil hydrological differences can be attributed to the impact of topography and hydrogeology. At the sloped site, conditions were generally wetter and less variable in time, and evidence was found for temporary lateral water transport along the slope. These differences were systematic and could be reduced by considering relative soil moisture changes. The application of a statistical landslide forecast model showed that both sites were equally able to distinguish critical from non-critical conditions for landslide triggering, which demonstrates the value of existing monitoring sites in flat areas for the application in LEWSs.

Ende August und Anfang Oktober 2020 waren die Südschweiz und angrenzende Bergkantone von zwei Unwettern betroffen, welche teils zu beträchtlichen Abflüssen, jedoch verhältnismässig geringen Schäden führten. Im Sinne einer Standortbestimmung wurden die beiden Unwetterereignisse zum Anlass genommen, das Funktionieren der Warnkette an der Schnittstelle zwischen den Bundesfachstellen und den Kantonen zu überprüfen. Zu diesem Zweck wurden die hydrometeorologischen Vorhersagen vor und während den beiden Unwettern sowie die daraus abgeleiteten Warnungen auf ihre Qualität und gegenseitige Abstimmung analysiert. Des Weiteren wurden mit Verantwortlichen der betroffenen Kantone Interviews geführt, um ihren Umgang mit den Warnungen und ihre Einschätzung zum Funktionieren der Warnkette zu erfahren. Schliesslich wurden in einem gemeinsamen Workshop potentielle Optimierungsmassnahmen erarbeitet.
Die Analysen und Rückmeldungen haben aufgezeigt, dass die Warnkette während den beiden Unwetterereignissen grundsätzlich gut funktioniert hat. In beiden Fällen war das Vorgehen der einzelnen Kantone bezüglich Informationsempfang, interner Beurteilung und Massnahmenentscheidungen sowie der Kontakt mit den Bundesstellen sehr unterschiedlich. Insgesamt wurde der Informationsfluss des Bundes während der beiden Ereignisse von den Kantonen als zielführend eingeschätzt. Die Analyse der Unwetter im August und Oktober 2020 hat aber auch punktuelle Optimierungsmöglichkeiten aufgezeigt und beispielsweise beim kommunikativen Zusammenspiel der Starkniederschlags- und Hochwasserwarnungen Fragen aufgeworfen.

A la fin août et au début octobre 2020, le sud de la Suisse et les cantons voisins ont été touchés par deux intempéries qui ont entraîné des débits parfois considérables, mais relativement peu de dégâts. Dans l'optique d'un état des lieux, ces deux événements ont été l'occasion de vérifier le fonctionnement de la chaîne d'alerte à l'interface entre les services spécialisés de la Confédération et les cantons. A cet effet, les prévisions hydrométéorologiques avant et pendant les deux intempéries, ainsi que les alertes qui en ont découlé, ont été analysées quant à leur qualité et leur coordination mutuelle. Par ailleurs, des entretiens ont été menés avec des responsables des cantons concernés afin de connaître leur gestion des alertes et leur évaluation du fonctionnement de la chaîne d'alerte. Enfin, des mesures d’optimisation potentielles ont été élaborées dans le cadre d'un séminaire commun.
Les analyses et les retours d'information ont montré que la chaîne d'alerte avait en principe bien fonctionné pendant les deux événements. Dans les deux cas, la procédure des différents cantons concernant la réception des informations, l'évaluation interne et les décisions relatives aux mesures, ainsi que le contact avec les services fédéraux, étaient très différents. Dans l'ensemble, les cantons ont estimé que le flux d’informations de la Confédération pendant les deux événements était conforme aux objectifs. Cependant, l'analyse des intempéries d'août et d'octobre 2020 a également montré des possibilités d'optimisation et soulevé des questions, par exemple concernant l'interaction en matière de communication entre les alertes aux fortes précipitations et aux crues.

In den 50 Jahren ihres Bestehens ermöglichte die Nationale Daueruntersuchung der Fliessgewässer (NADUF), zahlreiche Erfolge von Gewässerschutzmassnahmen in der Schweiz quantitativ zu belegen und Zustandsänderungen aufzuzeigen. Dazu gehören reduzierte Einträge von Phosphat, Schwermetallen oder Stickstoffverbindungen in die Gewässer. In der Zukunft stellen sich beim Monitoring neue Herausforderungen wie die Ermittlung der Einträge von organischen Mikroverunreinigungen oder die durch den Klimawandel induzierten Änderungen im aquatischen Ökosystem.

Hydropower (HP) is the backbone of the Swiss electricity system providing around 60% (36 TWh/a) of the total electricity generated on a yearly average. With the planned phase-out of nuclear power plants, HP and other Renewable Energy Sources (RES) will need to fill the substantial gap in domestic electricity generation, particularly in the winter season. Because of the intermittent nature of RES generation (mainly solar photovoltaics and wind) and their typically lower production in winter, the need for storage up to the seasonal time scale increases. Such large-scale storage is offered mainly by storage HP. However, maintaining the HP infrastructure will pose significant challenges, mainly due to market and legal conditions. For the latter, partly diverging interests according to the Swiss legislation will need to be fulfilled at the same time.
On the one hand, HP is supposed to be extended in the scope of the Energy Strategy (ES) 2050 and to keep climate goals by reducing greenhouse gas emissions. On the other hand, current negative effects of mainly older HP infrastructure on aquatic ecology will need to be remediated according to the Swiss Waters Protection Act to fulfill biodiversity goals. Meeting all these goals will require to systematically refurbish the existing Swiss HP fleet, to extend it in a smart way with prioritization on large storage HP to foster electricity generation in the critical winter season and to construct new HP schemes, again with a focus on electricity generation in winter.
As to new HP facilities, the retreating glaciers open new opportunities for high-altitude storage plants that, besides generating quasi CO₂-free electricity, have also other benefits like protection from natural hazards and water supply for irrigation. Extending existing storage lakes by heightening of their dams is a complementary option to create additional storage with generally low environmental impact and possibly higher public acceptance. [...]

Aufgrund des Klimawandels werden Schneedecke und Gletschermasse abnehmen, Niederschläge sich mehr in den Winter verschieben, und es muss mit häufigeren Sommertrockenheiten gerechnet werden. Gleichzeitig wird erwartet, dass die Nachfrage nach Wasser, insbesondere durch die Landwirtschaft, in den Sommermonaten zunehmen wird. In diesem Zusammenhang stellt sich die Frage, wie gross das Potenzial von Wasserspeichern zur Verminderung von Sommerwasserknappheit ist. In einem ersten Teilprojekt wurden für 307 mittelgrosse Einzugsgebiete der Schweiz die heutige und zukünftige Sommerwasserknappheit abgeschätzt und dem nutzbaren Speichervolumen natürlicher Seen und künstlicher Speicher gegenübergestellt. Dabei wurde aus Sicht der Wasserbilanz das lokale Potenzial von bestehenden Speichern zur Verminderung von Wasserknappheit als eher gering eingestuft. Auf regionaler Ebene (d.h., für grössere Einzugsgebiete) wurde jedoch aufgezeigt, dass ein Potenzial zur Verminderung der Wasserknappheit vorhanden ist. [...]

Due to climate change, snow cover and glacier mass will decrease, precipitation will shift more to the winter season, and more frequent summer droughts are to be expected. At the same time, the demand for water, especially for agriculture, is expected to increase in the summer months. In this context, the question arises how high the potential of water reservoirs is to reduce summer water shortages. In a first sub-project, the current and future summer water scarcity was estimated for 307 medium-sized catchments in Switzerland, and compared with the usable storage volume of natural lakes and artificial reservoirs. From a water balance perspective, the local potential of existing reservoirs to reduce water scarcity was found to be rather low. However, at the regional level (i.e. for larger catchments), it was shown that there indeed is a potential capacity to reduce water scarcity. [...]

Flood events are difficult to characterize if available observation records are shorter than the recurrence intervals, and the non-stationarity of the climate adds additional uncertainty. In this study, we use a hydrological model coupled with a stochastic weather generator to simulate the summer flood regime in two mountainous catchments located in China and Switzerland. The models are set up with hourly data from only 10–20 years of observations but are successfully validated against 30–40-year long records of flood frequencies and magnitudes. To assess the climate change impacts on flood frequencies, we re-calibrate the weather generator with the climate statistics for 2021–2050 obtained from ensembles of bias-corrected regional climate models. Across all assessed return periods (10–100 years) and two emission scenarios, nearly all model chains indicate an intensification of flood extremes. According to the ensemble averages, the potential flood magnitudes increase by more than 30% in both catchments. The unambiguousness of the results is remarkable and can be explained by three factors rarely combined in previous studies: reduced statistical uncertainty due to a stochastic modelling approach, hourly time steps and the focus on headwater catchments where local topography and convective storms are causing runoff extremes within a confined area.

When the observation of small headwater catchments in the pre‐Alpine Alptal valley (central Switzerland) started in the late 1960s, the researchers were mainly interested in questions related to floods and forest management. Investigations of geomorphological processes in the steep torrent channels followed in the 1980s, along with detailed observations of biogeochemical and ecohydrological processes in individual forest stands. More recently, research in the Alptal has addressed the impacts of climate change on water supply and runoff generation. In this article, we describe, for the first time, the evolution of catchment research at Alptal, and present new analyses of long‐term trends and short‐term hydrologic behaviour. Hydrometeorological time series from the past 50 years show substantial interannual variability, but only minimal long‐term trends, except for the ~2°C increase in mean annual air temperature over the 50‐year period, and a corresponding shift towards earlier snowmelt. Similar to previous studies in larger Alpine catchments, the decadal variations in mean annual runoff in Alptal's small research catchments reflect the long‐term variability in annual precipitation. In the Alptal valley, the most evident hydrological trends were observed in late spring and are related to the substantial change in the duration of the snow cover. Streamflow and water quality are highly variable within and between hydrological events, suggesting rapid shifts in flow pathways and mixing, as well as changing connectivity of runoff‐generating areas. This overview illustrates how catchment research in the Alptal has evolved in response to changing societal concerns and emerging scientific questions.

Current regional landslide Early Warning Systems (LEWS) are typically based on rainfall data and rarely use soil wetness information in spite of the direct relationship between soil wetness and landslide triggering. This is partly due to the limited availability of soil moisture measurement networks and the lack of experience in interpreting such data. Here we show how soil wetness measurements could be exploited for LEWS in a region (or country) with variable topography and soil composition. In particular, we highlight the relevance of (steep) topography for the soil wetness observations and its significance for the interpretation in regard to landslide criticality. To this end, a field study has been set up and is currently running in a landslide-susceptible region of central Switzerland (Emmental) where different soil wetness measurement methods are compared on a flat and a steep meadow site. First results suggest that in spite of noticeable topographical effects on soil drying and wetting the informative value of these data for LEWS is not very different for sloped and flat locations. Based on these findings and a comprehensive analysis of the co-occurrence between soil wetness indicators and shallow landslides across Switzerland we attribute soil wetness measurements a significant value for landslide early warning and encourage a wider incorporation of such data in existing warning systems.

The inclusion of soil wetness information in empirical landslide prediction models was shown to improve the forecast goodness of regional landslide early warning systems (LEWSs). However, it is still unclear which source of information - numerical models or in situ measurements - is of higher value for this purpose. In this study, soil moisture dynamics at 133 grassland sites in Switzerland were simulated for the period of 1981 to 2019, using a physically based 1D soil moisture transfer model. A common parameterization set was defined for all sites, except for site-specific soil hydrological properties, and the model performance was assessed at a subset of 14 sites where in situ soil moisture measurements were available on the same plot. A previously developed statistical framework was applied to fit an empirical landslide forecast model, and receiver operating characteristic analysis (ROC) was used to assess the forecast goodness. To assess the sensitivity of the landslide forecasts, the statistical framework was applied to different model parameterizations, to various distances between simulation sites and landslides and to measured soil moisture from a subset of 35 sites for comparison with a measurement-based forecast model. We found that (i) simulated soil moisture is a skilful predictor for regional landslide activity, (ii) that it is sensitive to the formulation of the upper and lower boundary conditions, and (iii) that the information content is strongly distance dependent. Compared to a measurement-based landslide forecast model, the model-based forecast performs better as the homogenization of hydrological processes, and the site representation can lead to a better representation of triggering event conditions. However, it is limited in reproducing critical antecedent saturation conditions due to an inadequate representation of the long-term water storage.

Gemäss verschiedenen Abschätzungen wird sich durch die Klimaveränderung nicht nur die Disposition für alpine Massenbewegungen, sondern auch deren Dynamik und die Interaktion von gravitativen Prozessen bzw. deren Verkettung in Prozesskaskaden verändern. Dies wird zu einem veränderten Risiko für die Schweizer Bevölkerung in Bezug auf alpine Massenbewegungen führen.
Das WSL Forschungsprogramm CCAMM - Climate Change Impacts on Alpine Mass Movements untersucht die Auswirkungen des Klimawandels auf alpine Massenbewegungen, um die daraus resultierenden Risiken besser abzuschätzen und geeignete Anpassungsstrategien für die Gesellschaft zu entwickeln. Im Folgenden stellen wir das WSL-Forschungsprogramm CCAMM vor.

Selon diverses estimations, le changement climatique modifiera non seulement la disposition des mouvements de masse alpins, mais aussi leur dynamique et l'interaction des processus gravitationnels ou leur enchaînement en cascade. Cela entraînera un changement de risque pour la population suisse par rapport aux mouvements de masse alpins.
Le programme de recherche du WSL CCAMM - Climate Change Impacts on Alpine Mass Movements - étudie les effets du changement climatique sur les mouvements de masse alpins afin de mieux évaluer les risques résultants et de développer des stratégies d'adaptation appropriées pour la société. Nous présentons ci-après le programme de recherche du WSL CCAMM.

Expansion of the hydrologically connected area during rainfall events causes previously disconnected areas to contribute to streamflow. If these newly contributing areas have a different hydrochemical composition compared to the previously connected contributing areas, this may cause a change in stream water chemistry that cannot be explained by simple mixing of rainfall and baseflow. Changes in stormflow composition are, therefore, sometimes used to identify when transiently connected areas (or water sources) contribute to stormflow. We identified the dominant sources of streamflow for a steep 20 ha pre-Alpine headwater catchment in Switzerland and investigated the temporal changes in connectivity for four rainfall events based on stream water concentrations and groundwater level data. First, we compared the isotopic and chemical composition of stormflow at the catchment outlet to the composition of rainfall, groundwater and soil water. Three-component end-member mixing analyses indicated that groundwater dominated stormflow during all events, and that soil water fractions were minimal for three of the four events. However, the large variability in soil and groundwater composition compared to the temporal changes in stormflow composition inhibited the determination of the contributions from the different groundwater sources. Second, we estimated the concentrations of different solutes in stormflow based on the mixing fractions derived from two-component hydrograph separation using a conservative tracer (δ²H) and the measured concentrations of the solutes in baseflow and rainfall. The estimated concentrations differed from the measured stormflow concentrations for many solutes and samples. The deviations increased gradually with increasing streamflow for some solutes (e.g. iron and copper), suggesting increased contributions from riparian and hillslope groundwater with higher concentrations of these solutes and thus increased hydrological connectivity. The findings of this study show that solute concentrations partly reflect the gradual changes in hydrologic connectivity, and that it is important to quantify the variability in the composition of different source areas.

Zukünftige Hochwasserereignisse sind schwer zu bemessen, besonders wenn deren Wiederkehrperioden länger sind als die Beobachtungsdauer von historischen Ereignissen. Im Rahmen einer laufenden chinesisch-schweizerischen Forschungszusammenarbeit zur Hochwasserbewältigung in kleinen bis mittleren Einzugsgebieten wurde eine Modellkette entwickelt, um Gefahrenhinweiskarten für zukünftige Hochwasser unter Berücksichtigung des Klimawandels zu erstellen. Die Anwendung der Modellkette in zwei Einzugsgebieten in China und in der Schweiz wird im nachfolgenden Beitrag diskutiert..

Les crues futures sont difficiles à quantifier, surtout si leur période de retour est plus longue que la période d'observation des événements historiques. Dans le cadre d'une actuelle recherche sino-suisse sur la gestion des inondations dans les bassins versants de petite à moyenne taille, une chaîne de modèles a été mise au point pour produire des cartes indicatives de danger pour les crues futures en tenant compte du changement climatique. L'application de la chaîne modèles dans deux bassins versants en Chine et en Suisse est examinée dans le présent article

Eine ausgeprägte Niederschlagsarmut im Sommer und Herbst des Jahres 2018 führte in grossen Teilen der Schweiz, insbesondere im nordöstlichen Mittelland, zu einer verbreiteten und lang anhaltenden Trockenheit. Die unmittelbaren und mittelfristigen Auswirkungen des trockenen Sommers 2018 auf Wachstum, Schädlingsund Krankheitsbefall und letztlich auf das Überleben vieler Bäume waren von bisher kaum beobachtetem Ausmass im Schweizer Wald. Nicht nur die Fichte, sondern auch die Buche und Mischwälder waren betroffen. Dabei wurden regionale und lokale Unterschiede festgestellt, die sich auch in der räumlichen Ausprägung des Niederschlags und der Bodentrockenheit manifestierten. Die teilweise massiven Auswirkungen führen vor Augen, dass Extremereignisse wie das Trockenjahr 2018 eine zentrale Rolle bei der klimabedingten Änderung der Waldzusammensetzung spielen können. Aus wissenschaftlicher Sicht gilt es daher, so viele Erkenntnisse und Lehren wie möglich aus diesen Extremereignissen zu ziehen, um adäquate, zukunftsgerichtete Waldbewirtschaftungskonzepte entwickeln zu können. Eine Forschungsinitiative der Eidgenössischen Forschungsanstalt für Wald, Schnee und Landschaft wurde genau mit diesem Ziel sehr kurzfristig im Laufe des Sommers 2018 lanciert. Der vorliegende Beitrag fasst wichtige Erkenntnisse im Hinblick auf die zukünftige Waldentwicklung zusammen.